KR20070060900A - Method for reducing heating time for catalyst gasoline engine - Google Patents

Abstract

A method for reducing heating time for a catalyst of a gasoline direct injection engine is provided to reduce back pressure by reducing the volume of the catalyst and the size of a cell. A method for reducing heating time for a catalyst of a gasoline direct injection engine includes a step of producing a lean fuel-air mixture by injecting 60~80% of the total fuel to the air sucked in a cylinder; and a step of producing a fuel-air mixture by injecting the remainder 20~40% to the vicinity of a recess hollow portion of a top surface of the piston.

Description

Reduction of catalyst heating time in gasoline direct injection engines {Method for reducing heating time for Catalyst Gasoline Engine}

1 is a block diagram of a gasoline direct injection engine to which the present invention is applied (excluding a cylinder and a piston),

2 is a perspective view showing a piston of a gasoline direct injection engine to which the present invention is applied;

3 is an explanatory diagram of a method for shortening the catalyst heating time of a gasoline direct injection engine according to the present invention;

Figure 4 is a graph of testing the air intake, ignition timing and catalyst temperature according to the method of the present invention,

5 is a graph showing the reduction of hydrocarbons and nitrogen oxides in the exhaust tested according to the method of the present invention.

<Description of the symbols for the main parts of the drawings>

30: injector 70: piston

72: concave cavity

The present invention relates to a method for shortening the catalyst heating time of a gasoline engine, and more particularly, to a method for shortening the catalyst heating time of a gasoline direct injection engine (GDI engine).

Gasoline engines can be divided into carburetor engines, multi-point injection (MPI) engines, and gasoline direct injection (GDI) engines according to fuel and air intake methods.

The carburettor engine is an engine in which a carburetor is coupled to the end of a nozzle connected to fuel, and when the air is sucked into the cylinder which is temporarily vacuumed during the intake stroke, the air pressure is lowered to spray the fuel through the carburetor. These engines not only reduce efficiency but also emit a lot of harmful exhaust gases, and as the electronic control technology for the engine is developed, it is rarely used at present.

The MPI engine is basically an engine with an injector on the outside of the engine. The injector at each inlet port is computer controlled, and the engine's state, including the temperature of the engine itself, and the driver's intention, that is, the accelerator pedal It is an engine that determines the amount of gasoline and injects it into the cylinder in consideration of the strength of the power. The MPI engine is currently the most used engine, and the carburettor engine needed to start the engine and heat it for about 10 minutes while the engine was frozen in winter, but the MPI engine could be started almost immediately. However, MPI engines are limited in fuel supply response and consumption control because they mix fuel and air before entering the cylinder.

 The GDI engine is a type of engine that directly injects gasoline by precisely adjusting the fuel injection amount and fuel injection timing through a computer-controlled nozzle in response to the intake of air, and by supplying a very thin mixer to enable combustion, The engine can achieve high performance and responsiveness over MPI engines because it can show excellent fuel efficiency and maintain a relatively high compression ratio due to its efficient intake structure. The GDI engine is in the spotlight as a next-generation engine that simultaneously satisfies low fuel consumption and high power.

On the other hand, since 90% of the total exhaust emission of the gasoline engine is discharged before the catalyst heating immediately after starting and starting, it is necessary to abate the exhaust gas at the start and to rapidly heat the catalyst after starting.

For MPI engines, the catalyst temperature is low for about 30 seconds after initial start-up, resulting in very low purging efficiency. In low temperature catalysts, hydrocarbons (HC) cannot be purified and are therefore all discharged within 30 seconds. In order to reduce the hydrocarbon (HC) it is essential to reduce the hydrocarbon by heating the catalyst quickly to reach the purification temperature. In the case of MPI engines, the catalyst is heated by delaying the ignition time within the range of combustion stability (about ATDC 10 degrees), but since the catalyst heating time is not shortened, about 70% of the total operating mode emissions are 30 Emitted within seconds.

In the case of the MPI engine, since the fuel is injected into the port, the injected fuel causes wall wetting to the partition wall, and thus, active flow strengthening using the partition wall and the like in the tumble port is impossible. Therefore, tumble flaps are used to enhance the flow upstream without the use of a dividing wall and to avoid wall wetting of the spray, but the tumble flow cancels the strength significantly as it reaches the valve.

In addition, due to the use of a homogeneous mixer that injects fuel from the port and introduces it into the cylinder, the concentration of the mixer around the plug is lean compared to stratified combustion, resulting in delayed ignition timing after a certain angle of TDC. . In the case of misfiring, unburned hydrocarbons (HC) are greatly increased, thus delaying the ignition timing within the limit of combustion stability. Due to these limitations, the cost of hydrocarbons is reduced due to the shortage of hydrocarbon (HC) within the initial 30 seconds.

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to increase the calorific value discharged to the exhaust gas during the start-up of the catalyst so that the catalyst heating time of the gasoline direct injection engine to reduce the hydrocarbon by heating the catalyst rapidly To provide a shortening method.

A method for shortening the catalyst heating time of a gasoline direct injection engine according to the present invention is a gasoline direct injection engine having a concave cavity recessed in an upper surface of a piston. 60 to 80% of the primary is injected into the combustion chamber and the cylinder to form a lean mixture as a whole, then when the piston reaches near top dead center (TDC), i.e. the remaining 20 to 40% at the end of the compression process, It is characterized by forming a mixer by secondary spraying in the vicinity of the part.

A dividing wall is formed in the middle of the cylinder port, and has a variable control module (VCM) which closes the lower surface of the port under the split wall during the catalytic heating operation so that flow is introduced only into the upper port. In the suction process, the VCM is closed and the bottom surface of the split wall is blocked to suck air into the cylinder only from the upper surface with a strong tumble flow.

Hereinafter, a method of shortening the catalyst heating time of the gasoline direct injection engine according to the present invention will be described in detail.

Fig. 1 is a system diagram of a GDI engine to which the present invention is applied. (The cylinder and the piston are not shown in the drawing.) As shown, the GDI engine includes a high pressure fuel gauge 10 and a low pressure fuel gauge 20 injector. 30, the injector 30 is to create an ideal injection shape (swirl shape) for the engine situation through the injector drive 50 controlled by the ECU (40). The high pressure pump 12 and the high pressure regulator 14 of the high pressure fuel gauge 10, the low pressure pump 22 and the low pressure regulator 24 of the low pressure fuel gauge 20 are required by the control of the ECU 40. Fuel is compressed to form high-pressure and low-pressure fuel in the fuel rail 60.

On the other hand, the GDI engine to which the present invention is applied has a tumble port which forms a tumble flow in the cylinder upon inhalation, has a split wall in the middle of the port, and divides the port up and down, and the port of the intake manifold and the head. VCM (variable control module), which is installed in the stub manifold between the inlets and closes the lower surface of the port under the split wall during catalyst heating operation so that the flow is introduced only into the upper port. The structure provided with) will be described as an example.

The closing of the split wall and the VCM in the tumble port enhances the flow to promote combustion (increase flame propagation speed, ignition delay and main combustion period) to increase combustion stability. And, as shown in Fig. 2, the piston 70 of the GDI engine is provided with a recessed recessed recess 72 in its upper surface to strengthen the introduced tumble flow and form a cylinder head and a combustion chamber. The fuel injected late in the split injetion forms a stable combustible mixer even during the exhaust process around the sparks.

In the GDI engine configured as described above, as shown in FIG. 3, in the suction process, the VCM is closed and the lower surface of the split wall is blocked to suck air into the cylinder only from the upper surface with a strong tumble flow.

60-80% of the total fuel (70%, the first injection air-fuel ratio is 21) is injected into the air being sucked during the suction process to form a lean mixer in the combustion chamber and the cylinder as a whole. This minimizes wall wetting and burns in the combustion chamber formed during the second half of compression.

Next, when the piston 70 reaches near the top dead center (TDC), i.e. at the end of the compression process, the remaining 20-40% (30%, the second injection air-fuel ratio is 48 when the total air-fuel ratio is 14.5) Secondary injection near the concave cavity 72 of the upper surface forms a mixer in which the air-fuel ratio combustion is stabilized only around the spark plug. In other words, a stratified mixer is formed around the spark plug. Such a mixer maintains a combustible mixer early in the expansion process in which the piston moves downward. Therefore, the ignition delay time during which the combustion is stabilized during the expansion process is extended. After ignition, flames initially form locally in the combustible mixer around the plug and propagate to the edge mixer.

The delay of the ignition timing can increase the amount of air sucked in the same torque base, so that the total amount of heat generated by the fuel is greatly increased at the same air-fuel ratio. That is, it is possible to perceive the ignition timing very largely by stable combustion and increase the calorific value in the exhaust gas, as shown in the graph of FIG. 4, the temperature before the catalyst increases greatly from about 2 seconds after the start of operation, and after about 15 seconds, it is about 400 ° C. There is a difference.

A large amount of calorific value introduced into the catalyst can be heated to a temperature that can be purified within the time to suck the cold catalyst after the initial start-up can significantly reduce the hydrocarbon (HC) emitted from the engine in the catalyst.

 As shown in Fig. 5, according to the present invention, the amount of heat generated by the exhaust gas at the time of heating the catalyst is increased so that the catalyst is heated within a short time (15 to 30 seconds after startup) to be discharged within the initial 60 seconds. It is possible to reduce the hydrocarbon (90% emission during the mode operation) by more than 40%, and also take advantage of the freedom of changing the ignition timing, and slightly increase the hydrocarbon (HC) emission by slightly pulling the ignition timing during the mode operation. Oxide (NOx) reduction is possible.

4 and 5 are graphs in which 70% of the total fuel is injected during the primary fuel injection and 30% of the total fuel is injected during the secondary fuel injection.

According to the method for shortening the catalyst heating time of a gasoline direct injection engine according to the present invention, a hydrocarbon is reduced by rapidly heating the catalyst by increasing the calorific value discharged to the exhaust during the catalyst heating time at start-up, thereby reducing the catalyst volume and reducing the cell. The back pressure (within about 5 Kpa) is reduced due to size reduction, and the performance is improved, and the degree of freedom in installing an exhaust system in a vehicle is increased. In addition, the cost is reduced because the increase in the amount of catalyst or precious metal used in the past is reduced.

Claims (2)

A gasoline direct injection engine having a concave cavity recessed in an upper surface of a piston, After injecting 60 to 80% of the total fuel into the air being sucked into the upper surface of the cylinder during the suction process, a lean mixer is formed in the combustion chamber and the cylinder as a whole. A method of shortening the catalyst heating time of a gasoline direct injection engine, characterized in that to form a mixer by injecting the remaining 20 to 40% at the end of the compression process in the vicinity of the concave cavity of the upper surface of the piston. The method of claim 1, A dividing wall is formed in the middle of the cylinder port, and has a variable control module (VCM) which closes the lower surface of the port under the split wall during the catalytic heating operation so that flow is introduced only into the upper port. , The method of reducing the catalyst heating time of the gasoline direct injection engine, characterized in that in the intake process closes the VCM and blocks the lower surface of the split wall to suck air into the cylinder only from the upper surface with a strong tumble flow.

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